1. Field of the Invention
The present invention relates to an electric power steering apparatus and a method of controlling the same.
2. Description of the Prior Art
A hydraulic steering apparatus is configured such that a hydraulic pump, which is a power source for supplying a steering assist power, is driven by an engine. Thus, the hydraulic steering apparatus always consumes energy regardless whether the steering wheel is rotated or not. Whereas, an electric power steering apparatus is configured such that, when a steering torque is produced by the rotation of the steering wheel, a motor supplies a steering assist power which is proportional to the produced steering torque. Accordingly, when the electric power steering apparatus is used, the energy efficiency may be improved as compared to the case where the hydraulic steering apparatus is used.
The electric power steering apparatus is configured such that the steering torque produced by the rotation of the steering wheel is transmitted to a rack bar through a rack-and-pinion mechanism and the steering assist power produced in the motor according to the produced steering torque is transmitted to the rack bar. That is, the steering torque produced by the steering wheel and the steering assist power produced in the motor are combined to move the rack bar in the axial direction.
Such an electric power steering apparatus suffers from a change of a mechanical characteristic as the traveled distance equipped with the electric power steering apparatus increases. When manufacturing a steering apparatus, a tuning value is tuned based on a new element. However, when the mechanical characteristic is changed, e.g., when an element of the electric power steering apparatus becomes worn out as the electric power steering apparatus is operated, a problem may occur in that the tuning value tuned at the time of manufacturing becomes incorrect.